1. Field of the Invention
This invention relates to an electric circuit for use in a liquid crystal display apparatus and the like, in which an electrode pattern arranged on a glass substrate is connected to a conductive pattern on a flexible insulating film.
2. Description of Related Art
FIG. 1 is a perspective view of a conventional liquid crystal display apparatus using a flexible printed circuit (FPC) disclosed, for example, in the Japanese Patent Application Laid-Open No. 1-253791 (253791/1989). A liquid crystal panel 1 is constituted of two glass substrates 2 facing each other and a liquid crystal sealed between the glass substrates 2. The glass substrates 2 are provided in a manner that the electrode patterns arranged in stripes thereon intersect each other.
On the three sides of the liquid crystal display panel 1, plural FPC substrates 21 of insulating films with IC chips thereon for supplying signals to the electrodes are provided. On the rest one side of the liquid crystal display panel 1, an FPC substrate 22 of an insulating film for connecting the gate bus lines formed on the upper and lower halves of the liquid crystal display panel 1.
FIG. 2 is a plane view of a conventional insulating film with a conductive pattern formed thereon by the tape automated bonding (TAB) disclosed in the Japanese Patent Application Laid-Open No. 2-74922 (74922/1990), for instance. One ends of input terminals 25 and output terminals 26 formed on a base film 23 are connected to an IC chip 24, with the other ends thereof being connected to an electrode pattern formed on a glass substrate (not shown). In this case, the output terminals 26 are connected to the electrode pattern on the glass substrate by means of an anisotropic conductive film as depicted, e.g., in the Japanese Patent Application Laid-Open Nos. 2-22694 (22694/1990), 2-46426 (46426/1990) and the Japanese Utility Model Application Laid-Open No. 2-33032 (33032/1990).
FIG. 3 is a plane view of another insulating film having a conductive pattern formed thereon through TAB, disclosed, e.g., in the Japanese Utility Model Application Laid-Open No. 2-51322 (51322/1990). Similar to the above example of FIG. 2, one ends of input terminals 25 and output terminals 26 formed on a base film 23 are connected to an IC chip 24, and the other ends thereof are connected to an electrode pattern on a glass substrate (not shown). The output terminals 26 and electrode pattern on the glass substrate are connected with each other through soldering as described, for example, in the Japanese Utility Model Application Laid-Open No. 2-119150 (119150/1990).
The operation of the conventional electric circuit as aforesaid will be explained hereinafter.
In the liquid crystal display apparatus of FIG. 1, the displaying data generated by the IC chip 24 on the FPC substrate 21 is fed to source bus lines, so that the impressed voltage to the liquid crystals changed the transmittance or color of the liquid crystal panel 1, thereby obtaining the aimed images.
Meanwhile, as indicated in FIG. 2, the IC chip 24 on the base film 23 is connected to the input and output terminals 25 and 26 via electrodes, and the IC chip 24 outputs an image signal to the output terminal 26 on the basis of an input signal from the input terminal 25.
Also in FIG. 3, the IC chip 24 mounted on the base film 23 generates the data inputted to the input terminal 25 to the terminal 26 as an image signal for each pixel.
In the aforementioned structure of the electric circuit employed hitherto in the liquid crystal display apparatus, in the case where the FPC substrates 21, 22 and base film 23 are polyimide, although the nominal coefficient of linear expansion of polyimide is 20.times.10.sup.-6 and larger than that of glass, 9.times.10.sup.-6, the difference of the coefficients of linear expansion does not matter when the output terminal of the FPC substrate or TAB film, namely, a connected part to the electrode pattern on the glass substrate 2 is relatively short. However, when an increase in the number of output signals from each IC chip 24 or a plurality of IC chips 24 mounted to a single FPC substrate or TAB film (multi-chip TAB) elongates the part connected to the electrode pattern on the glass substrate 2, it becomes a problem.
In other words, when the connected part is exposed to the heat cycle generated by the power of the apparatus being turned ON or OFF, the bond strength at the connected part reduces due to the thermal stress resulting from the difference of the coefficients of linear expansion, thereby increasing the resistance against connection, or in extreme case, leading to a disconnection.